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On internal medicine rounds, the attending is reviewing the myocardial action potential. In which of the following phases of the action potential do the voltage-gated potassium channels begin to open?

A. Phase 0
B. Phase 1
C. Phase 2
D. Phase 3
E. Phase 4

i need an explanation,please.


phase 3...actually some k+efflx will be there during phase 1...but voltage gated k+channels open in phase 3..if i am wrong correct me


they begin to open in phase 1..


Asmi, could you explain in few words what's happened in each fase, please.



V-g=Voltage gated

• Increase Na+ Conductance
• Fast Na+ Channels (V-g) open during Depolarization--> quick Na+ influx

Phase 1 - Slight Repolarization
• Due to special K+ Channel: efflux through V-g K+ Channels

Phase 2 - Plauteau phase
• Slow (V-g) channels of Ca++ open; increasing Calcium conductance • Calcium influx occurs
o Participate in contraction
o Release additional Ca++ from Sarcoplasmic Reticulum
o Very low K+ conductance resulting in Delayed Repolarization and stable plateau (b/c V-g K+ Channels are closed; there is like an equilibrium : Ca influx and K efflux--> "Plateau" )

Phase 3 - Repolarization
• V-g Ca++ Channels close
• V-g K+ Channels REOPEN; increasing K+ conductance
• Massive K+ efflux

Phase 4 - Resting State 8)
In regular contracting ventricle fibers, we have a stable resting membrane potential (Em)

That's it :wink:


wow kris :icon_salut:


thank you so much...
you save my nerves. smiling face

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